The present invention relates to gas or combustion turbine apparatus, gas turbine electric power plants and control systems and operating methods therefor.
Industrial gas turbines may have varied cycle, structural and aerodynamic designs for a wide variety of uses. For example, gas turbines may employ the simple, regenerative, steam injection or combined cycle in driving an electric generator to produce electric power. Further, in these varied uses the gas turbine may have one or more shafts and many other rotor, casing, support, and combustion system structural features which can vary relatively widely among differently designed units. They may be aviation jet engines adapted for industrial service as described for example in an ASME paper entitled "The Pratt and Whitney Aircraft Jet Powered 121MW Electrical Peaking Unit" presented at the New York Meeting in November-December 1964.
Other gas turbine uses include drive applications for pipeline or process industry compressors and surface transportation units. An additional application of gas turbines is that which involves recovery of turbine exhaust heat energy in other apparatus such as electric power or industrial boilers or other heat transfer apparatus. More generally, the gas turbine air flow path may form a part of an overall process system in which the gas turbine is used as an energy source in the flow path.
Gas turbine electric power plants are usable in base load, mid-range load and peak load power system applications. Combined cycle plants are normally usable for the base or mid-range applications while the power plant which employs a gas turbine only as a generator drive typically is highly useful for peak load generation because of its relatively low investment cost. Although the heat rate for gas turbines is relatively high in relation to steam turbines, the investment savings for peak load application typically offsets the higher fuel cost factor. Another economic advantage for gas turbines is that power generation capacity can be added in relatively small blocks such as 25MW or 50MW as needed for expected system growth thereby avoiding excessive capital expenditure and excessive system reserve requirements. Further background on peaking generation can be obtained in articles such as "Peaking Generation" a Special Report of Electric Light and Power dated November 1966.
Startup availability and low forced outage rates are particularly important for peak load power plant applications of gas turbines. Thus, reliable gas turbine startup and standby operations are particularly important for power system security and reliability.
In the operation of gas turbine apparatus and electric power plants, various kinds of controls have been employed. Relay-pneumatic type systems form a large part of the prior art. More recently, electronic controls of the analog type have been employed as perhaps represented by U.S. Pat. No. 3,520,133 entitled Gas Turbine Control System and issued on July 14, 1970 to A. Loft or by the control referred to in an article entitled Speedtronic Control, Protection and Sequential System and designated as GER-2461 in the General Electric Gas Turbine Reference Library. A wide variety of controls have been employed for aviation jet engines including electronic and computer controls as described for example in a March 1968 ASME Paper presented by J. E. Bayati and R. M. Frazzini and entitled "Digatec (Digital Gas Turbine Engine Control)", an April 1967 paper in the Journal of the Royal Aeronautical Society authored by E. S. Eccles and entitled "The Use of a Digital Computer for On-Line Control of a Jet Engine", or a July 1965 paper entitled "The Electronic Control of Gas Turbine Engines" by A. Sadler, S. Tweedy and P. J. Colburn in the July 1965 Journal of the Royal Aeronautical Society. However, the operational and control environment for jet engine operation differs considerably from that for industrial gas turbines. In referencing prior art publications or patents as background herein, no representation is made that the cited subject matter is the best prior art.
Generally, the operation of industrial gas turbine apparatus and gas turbine power plants have been limited in flexibility, response speed, accuracy and reliability. Further limits have been in the depth of operational control and in the efficiency or economy with which single or multiple units are placed under operational control and management. Limits have existed on the economics of industrial gas turbine application and in particular on how close industrial gas turbines can operate to the turbine design units over various speed and/or load ranges.
In gas turbine power plants, operational shortcomings have existed with respect to plant availability and load control operations. Turbine surge limit control operations have been limited particularly during startup. Temperature limit control has been less protective and less responsive than otherwise desirable.
Generally, overall control loop arrangements and control system embodiments of such arrangements for industrial gas turbines have been less effective in operations control and systems protection than is desirable. Performance shortcomings have also persisted in the interfacing of control loop arrangements with sequencing controls.
With respect to industrial gas turbine startup, turbine operating life has been unnecessarily limited by conventional startup schemes. Sequencing systems have typically interacted with startup controls less effectively than desirable from the standpoint of turbine and power plant availability. More generally, sequencing systems have provided for systematic and protective advance of the industrial gas turbine operations through startup, run and shutdown but in doing so have been less efficient and effective from a protection and performance standpoint than is desirable.
Restrictions have been placed on operations and apparatus management particularly in gas turbine power plants in the areas of maintenance and plant information acquisition. Further management limits have existed with respect to plant interfacing with other power system points, operator panel functionality, and the ability to determine plant operations through control system calibration and parameter changes.